How to Compare strings by Regex inside a LINQ Query? - regex

Question

I have two datatables dtRosterList and falsefields
I want to list out all rosterlist against falsefields ,where list column value is a sentence "Hello i am a list of field" and falsefields column value having a single string "field"...i am matching by Regex.IsMatch
Regex.IsMatch(r.Field<string>("ListName"),#"\bFacebook Link\b")
is returning true in the Visual studio intermediate window but
Regex.IsMatch(r.Field("ListName"),#"\b"+fn+"\b") is coming false in Linq query itself and i am getting no rows...The query is below:
var listTobeDeleted = dtRosterList.AsEnumerable().
Where(r => falsefields.AsEnumerable()
.Select(f => f.Field<string>("FieldName")).Any(fn => Regex.Match(r.Field<string>("ListName"),#"\b"+fn+"\b",RegexOptions.IgnoreCase))).CopyToDataTable();

Answer 1

Two problems with your code:
You've used Regex.Match instead of Regex.IsMatch;
You've missed the # verbatim string literal prefix on the second "\b" string;
With the prefix, the string contains two characters: \ (ASCII code 92), and b (ASCII code 98). The Regex engine interprets this to mean "the match must occur on a boundary between an alphanumeric and a non-alphanumeric character".
Without the prefix, the string contains a single character: backspace (ASCII code 8). The Regex engine interprets this as a literal character, and so will only match a string containing the backspace character.
I'd also be inclined to add a Regex.Escape call around the word to find, in case it contains any special characters.
var listTobeDeleted = dtRosterList.AsEnumerable()
.Where(r => falsefields.AsEnumerable()
.Select(f => f.Field<string>("FieldName"))
.Any(fn => Regex.IsMatch(r.Field<string>("ListName"), #"\b" + Regex.Escape(fn) + #"\b", RegexOptions.IgnoreCase)))
.CopyToDataTable();